How do I curve a brick mesh into a hexagonal shape?
You can still use the curve modifier, you just need a hexagonal curve.

Enable the 'Extra Objects' for curves addon by going to File> User Preferences> Addons> Add Curve> Extra Objects and ticking the checkbox.

The 'Add' menu now has extra objects, choose 'Curves Galore!'



Choosing 'Nsided' from the tool panel (T) and setting 'Sides' 6 will produce a hexagonal curve



You can then add several array modifiers on the brick before the curve modifier to create the rows of bricks.

I have also placed a 'Subsurf' modifier set to 'Simple' subdivision as the first modifier so that the bricks have a little more resolution to curve around the corners.